Radio communication apparatus

ABSTRACT

A communication apparatus operating under a back scattering system involving processes of QPSK modulation is provided. The apparatus includes: a first signal channel for acquiring a first reflected wave by getting an incoming radio wave directly reflected without wave passage through any phase shifter; a second signal channel for acquiring a second reflected wave having a phase shifted by π/2 relative to the phase of the first reflected wave through two-way wave passage through a first phase shifter alone; a third signal channel for acquiring a third reflected wave having a phase shifted by π relative to the phase of the first reflected wave through two-way wave passage through the first and a second phase shifter; and a fourth signal channel for acquiring a fourth reflected wave having a phase shifted by 3π/2 relative to the phase of the first reflected wave through two-way wave passage through the first through a third phase shifter.

TECHNICAL FIELD

The present invention relates to a wireless communication apparatusoperating under a radio communication system that uses microwaves over aspecific frequency band. More particularly, the invention relates to awireless communication apparatus for communicating on a low level ofpower with an apparatus at a relatively close location.

Furthermore, the present invention relates to a wireless communicationapparatus that permits data communication over relatively shortdistances by use of a back scattering system by taking advantage of theabsorption and reflection of received radio waves based on the operationof antenna termination. In particular, the invention relates to awireless communication apparatus for boosting the transmission rate ofback scattering type data communication through a modulating process athigher bit rates than before.

BACKGROUND ART

RFID (radio frequency identification) is one typical means of locallyusable wireless communication. RFID is implemented as a system primarilymade up of tags and a reader, the reader reading information off eachtag in noncontact fashion. Also called an ID system or a data carriersystem, RFID is a recognition system that utilizes radio frequencies(radio waves). Communication between a tag and a reader/writer iseffected by diverse methods including electromagnetic coupling,electromagnetic induction, and radio frequency communication (refer toNon-Patent Document 1)

An RFID tag is a device that contains specific identificationinformation. In operation, the tag generates radio waves at a modulationfrequency corresponding to the identification information upon receiptof radio waves on a particular frequency. The reader having read theRFID tag can determine its identity based on its oscillation frequency.It follows that an RFID-based system allows goods carrying RFID tags orowners of the goods to be identified using particular IDs written in thetags. At present, RFID is applied to numerous systems such as entry/exitmanagement systems for managing people's comings and goings into and outof a controlled room, article identification systems deployed in thedistribution industry, bill settlement systems at cafeterias, and theftprevention systems at retailers handling CDs and software products.

Illustratively, it is possible to build an IC chip having capabilitiesfor data transmission and reception as well as data storage, a powersource for driving the chip, and an antenna into a small-sized wirelessidentification apparatus in packaged form (refer to Patent Document 1).With this wireless identification apparatus in use, various items ofdata on goods and articles are transmitted via the antenna to receivingmeans of the IC chip. The transmitted data can be stored in a memory ofthe chip and can be output wirelessly to the outside via the antenna.This makes it possible for goods or articles carrying the chip to betracked down and identified for their presence and location.

FIG. 9 shows a typical configuration of a conventional RFID system.Reference numeral 101 denotes an RFID tag constituted by a tag chip 102and an antenna 103. The antenna 103 may illustratively be a half-wavedipole antenna. The tag chip 102 is made up of a modulation unit 110, arectification/demodulation unit 112, and a memory unit 113.

A radio wave f₀ transmitted from a tag reader 100 is received by theantenna 103 before being input to the rectification/modulation unit 110.The unit 110 rectifies the received radio wave f₀ into a direct currentthat triggers a demodulation function. The radio wave is thus recognizedas a readout signal from the tag 101. The power generated by receptionof the radio wave f₀ is also fed to the memory unit 113 and modulationunit 110.

The memory unit 113 reads ID information previously stored internallyand sends the retrieved information to the modulation unit 110 asoutgoing data. The modulation unit 110, composed of a diode switch 111,turns on and off the switching action repeatedly in keeping with a bitimage of the outgoing data. More specifically, when the data is “1,” thediode switch 111 is turned on to terminate the antenna at antennaimpedance (e.g., at 50 ohms). At this point, the radio wave from the tagreader 100 is absorbed. When the data is “0,” the diode switch 111 isturned off (i.e., opened) to terminate the antenna in an open state. Atthis point, the radio wave from the tag reader 100 is reflected and sentback to where it came from. The reflection-absorption pattern of theincoming radio wave represents data in what is known as the backscattering system. In this manner, the tag 101 can transmit its internalinformation without dissipating power.

The tag reader 100 is constituted by a host device 106 such as a PDA, atag reader module 104, and an antenna 105 connected to the tag readermodule 104.

The host device 106 sends a read command from the tag 101 to acommunication control unit 119 via a host interface unit 120. Uponreceipt of the read command from the host interface unit 120, thecommunication control unit 119 edits outgoing data in a predeterminedmanner, filters the edited data, and sends the filtered data to an ASKmodulation unit 117 as a base band signal. The ASK modulation unit 117carries out ASK (amplitude shift keying) modulation by use of afrequency f₀ of a frequency synthesizer 116.

The frequency synthesizer 116 sets the frequency under control of thecommunication control unit 119. Generally, the transmission frequency toan RF tag is determined through hopping so as to reduce standing wavesand multipath interference in the signal coming from the tag. A hoppingcommand is also given by the communication control unit 119. An outgoingsignal having undergone ASK modulation is forwarded to a circulator 114before being emitted to the tag 101 from the antenna 105.

The tag 101 returns a signal at the same frequency as that of the signalcoming from the tag reader 100 by the effect of reflection through backscattering (as described above). The returned signal is received by theantenna 105 of the tag reader 100 and input to a mixer 115. Because themixer 115 admits the same local frequency f₀ as that of the outgoingsignal, a signal modulated by the tag 101 appears at the output of themixer 115. A demodulation unit 118 demodulates data formed by 1's and0's out of the signal and forwards the data to the communication controlunit 119. The communication control unit 119 decodes the data so as toacquire ID data that was held in the memory unit 113 inside the tag 101,and transfers the ID date through the host interface unit 120 to thehost device 106.

In the above-described setup, the tag reader 100 can read informationfrom inside the tag 101. The tag reader 100 generally doubles as a tagwriter that can be used to write the data designated by the host device106 into the memory unit 113 in the tag 101.

Conventionally, the above-described kind of back scattering typewireless communication system tags has been applied mainly to theidentification and recognition of articles and persons typically throughthe use of RFID tags. That is because the range of communication by thecommunication system has been limited to relatively short distances.

Meanwhile, back scattering type wireless communication has the potentialfor providing wireless transmission channels at a very low level ofpower dissipation as long as the communication distance is limited.Recent years have witnessed the advent of IC chips carrying memoryfunctions thanks to improved packaging techniques, with the memorycapacity getting larger over time. Such developments have aroused theneeds not only for the communication of identification and recognitioninformation over relatively short distances but also for general datatransmission applications based on back scattering type communication.

However, conventional back scattering type communications systems havefailed to offer high data transmission rates necessary for generalapplications. That is because they operate on the principle of ASK(amplitude shift keying) or BPSK (binary phase shift keying), i.e.,modulation methods of relatively low bit rates.

[Patent Document 1]

Japanese Patent Laid-open No. Hei 6-123773

[Non-Patent Document 1]

“RFID Handbook: the Principle and Applications of Noncontact IC Cards”(by Klaus Finkenzeller, translated into Japanese by Soft KogakuKenkyusho Ltd., and published by The Nikkan Kogyo Shimbun Ltd.).

DISCLOSURE OF INVENTION

[Problems to be Solved by the Invention]

It is therefore an object of the present invention to provide a wirelesscommunication apparatus for carrying out data communicationadvantageously over relatively short distances under a back scatteringsystem taking advantage of the absorption and reflection of receivedradio waves based on the operation of antenna termination.

It is another object of the present invention to provide a wirelesscommunication apparatus for boosting the transmission rate of backscattering type data communication through a modulating process athigher bit rates than before.

[Means For Solving the Problems]

In carrying out the invention and according to a first aspect thereof,there is provided a wireless communication apparatus for performing datacommunication under a back scattering system using reflection ofincoming radio waves, the wireless communication apparatus including adata transmission unit including: an antenna for receiving an incomingradio wave from a data transfer destination; as many as n signalchannels wherein a k-th signal channel gives a phase difference of(k−1)λ/2^(n−1) for one-way wave passage therethrough, where 1≦k≦n; andreflected wave forming means for forming reflected waves with as many asn different phases, by selecting any one of the signal channels inkeeping with outgoing data; wherein the data transmission unit forms theoutgoing data using a phase difference pattern of the reflected waveswith regard to the incoming radio wave.

Preferably, the wireless communication apparatus of the above structuremay further include a first through an (n−1)th phase shifter each givinga phase difference of λ/2^(n+1) for one-way wave passage therethrough,the phase shifters being connected in series to the antenna. The nsignal channels may preferably include a first signal channel foracquiring a first reflected wave by getting the incoming radio wavedirectly reflected without wave passage through any of the phaseshifters, and a k-th signal channel for acquiring a k-th reflected wavehaving a phase shifted by (k−1)π/2^(n−1) relative to the phase of thefirst reflected wave through two-way wave passage between the firstphase shifter and a (k−1)th phase shifter, where 1≦k≦n.

The reflected wave forming means may preferably perform 2^(n) phase PSKmodulation by dividing the outgoing data into increments of 2^(n−1) bitseach and by assigning phases to the reflected waves through selection ofa signal channel in keeping with combinations of 0's and 1's in the2^(n−1) bits.

Preferably, the wireless communication apparatus of the above structuremay further include a first through an n-th reflection point locatedbetween the antenna and the first phase shifter, between the (k−t)thphase shifter and the k-th phase shifter where 2≦k≦n−1, and downstreamof the (n−1)th phase shifter. Each of the reflection points mayillustratively be formed either by grounding or by use of an opentermination.

The reflected wave forming means may preferably perform 2^(n) phase PSKmodulation by dividing the outgoing data into increments of 2^(n−1) bitseach and by assigning phases to the reflected waves through switching ofthe reflection points in keeping with combinations of 0's and 1's in the2^(n−1) bits.

Where the invention is practiced as outlined above, wireless datatransmission is carried out using a back scattering system thatimplements QPSK modulation where n=2.

In another preferred structure according to the invention, the wirelesscommunication apparatus may further include a first through a thirdphase shifter each giving a phase difference of λ/8 for one-way wavepassage therethrough, the phase shifters being connected in series tothe antenna; wherein the n signal channels may include: a first signalchannel for acquiring a first reflected wave by getting the incomingradio wave directly reflected without wave passage through any of thephase shifters; a second signal channel for acquiring a second reflectedwave having a phase shifted by π/2 relative to the phase of the firstreflected wave through two-way wave passage through the first phaseshifter alone; a third signal channel for acquiring a third reflectedwave having a phase shifted by π relative to the phase of the firstreflected wave through two-way wave passage through the first and thesecond phase shifters; and a fourth signal channel for acquiring afourth reflected wave having a phase shifted by 3π/2 relative to thephase of the first reflected wave through two-way wave passage throughthe first through the third phase shifters.

For example, if the data divided into two bits is “00,” the first signalchannel may be selected. If the data is “01,” the second signal channelmay be selected to acquire a reflected wave with its phase shifted by 90degrees relative to the phase in effect when the data is “00.” If thedata is “10,” the third signal channel may be selected to acquire areflected wave with its phase shifted by 180 degrees relative to thephase in effect when the data is “00.” If the data is “11,” the fourthsignal channel may be selected to acquire a reflected wave with itsphase shifted by 270 degrees relative to the phase in effect when thedata is “00.” In this manner, it is possible to generate four reflectedwaves with four different phases 90 degrees apart from one another inaccordance with the varying combination of two-bit data. This methodprovides reflected waves through QPSK modulation.

Preferably, the reflected wave forming means may perform PSK modulationusing solely the first and the third signal channels.

In addition to data transmission applications, a method for generatingpolyphase modulated waves according to this invention is effective whenused in general RFID applications in which no power source is provided.Illustratively, the wireless communication apparatus may further includea data reception unit constituted by a filter for allowing the incomingradio wave received by the antenna to pass on a predetermined frequencyband, and by a data reception unit including a wave detection unit forforming a signal; wherein the data transmission unit and the datareception unit may be switched alternately depending on whether or notthe outgoing data is transmitted. With this structure, the incomingradio wave from the antenna can be input to the wave detection unit witha minimum of losses through switching devices such as radio frequencyswitches and a band-pass filter.

According to a second aspect of the invention, there is provided awireless communication apparatus for performing data communication undera back scattering system using reflection of incoming radio waves, thewireless communication apparatus including a data transmission unitincluding: an antenna for receiving an incoming radio wave from a datatransfer destination; a first reflected signal channel made of a firstradio frequency switch; a second reflected signal channel made of phasemodulating means giving a phase difference of λ/8 and a second radiofrequency switch; serial/parallel converting means for convertingoutgoing data from serial form into a parallel signal; andsynthesizing/distributing means for distributing the incoming radio wavecoming from the antenna to the reflected signal channels and forsynthesizing outputs from the reflected signal channels; whereinactivation and deactivation of each of the radio frequency switches arecontrolled using two data items constituting the data having undergonethe serial/parallel conversion, so that the data transmission unit formsthe outgoing data using a phase difference pattern of the reflectedwaves with regard to the incoming radio wave.

Where the wireless communication apparatus according to the secondaspect of the invention is in use, two radio frequency switches areturned on and off so that one radio frequency switch incorporating abinary phase modulator generates a reflected signal with its phaseshifted by λ/8 relative to the phase of another reflected signalgenerated by the other radio frequency switch. The apparatus thusgenerates outgoing data through four-phase PSK modulation under on-offcontrol based on two data items converted from serial to parallel form.

With the above structure, the first reflected signal channel made of thefirst radio frequency switch functions as a BPSK modulator, and thesecond reflected signal channel made of the binary phase modulator andsecond radio frequency switch acts as another BPSK modulator. The latterBPSK modulator, with its binary phase modulating mean, provides a phasedelay of λ/8 for one-way wave passage and a phase change of λ/4 fortwo-way wave passage. It follows that the latter BPSK modulator performsBPSK modulation on an axis that has a 90-degree phase difference withregard to the former BPSK modulator. This arrangement is equivalent toone which carries out QPSK modulation. That is because the firstreflected signal channel performs BPSK modulation on the I axis whilethe second reflected signal channel executes BPSK modulation on the Qaxis. In this case, the synthesizing/distributing means is used todivide the received radio wave into two branches and to synthesize thedivided parts.

In the manner described, the incoming radio wave from the antenna isdivided into two carriers by the synthesizing/distributing means beforebeing subjected to QPSK modulation by the first and the second reflectedsignal channels. The reflected signals thus modulated are passed throughthe synthesizing/distributing means before being emitted again from theantenna.

The serial/parallel converting means converts the outgoing data fromserial to parallel form, i.e., to a parallel signal of I and Q.

EFFECT OF THE INVENTION

According to the invention, as described, there is provided a wirelesscommunication apparatus for communicating data advantageously overrelatively short distances under the back scattering system utilizingabsorption and reflection of received radio waves through operation ofantenna termination.

The invention provides a wireless communication apparatus forcommunicating data under the back scattering system at highertransmission rates than before by means of a modulation method atimproved bit rates such as QPSK modulation.

The invention also provides a wireless communication system and awireless communication apparatus for wirelessly transferring picturedata from portable devices such as digital cameras or cellular phones toPCs, televisions, printers or the like with a minimum of powerdissipation.

The invention further provides a wireless communication system and awireless communication apparatus for mostly transmitting data from onedevice to another located a relatively short distance apart with aminimum of power dissipation.

The invention thus offers arrangements for implementing a mobile devicecapable of transmitting picture data while realizing order-of-magnitudesavings in power dissipation as compared with wireless LAN setups. Suchinventive arrangements make it possible to boost the battery life ofmobile devices considerably.

Furthermore, the invention permits easy implementation of a wirelesstransmission module as a data transmitter for a mobile device at anappreciably lower cost than wireless LAN alternatives. Such wirelesstransmission modules in the mobile device are not regarded as wirelessstations under the Radio Law of Japan. That means there is no need foraddressing the chores of requesting and obtaining permits such asConformity Certificates from the competent authorities.

Other objects, features and advantages of the invention will become moreapparent upon a reading of the following description and appendeddrawings.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of this invention will now be described in detailwith reference to the accompanying drawings.

This invention provides primarily a wireless communication setup formostly transmitting data from one device to another located a relativelyshort distance apart with a minimum of power dissipation. According tothe invention, wireless data transmission is implemented by use ofreflected waves derived from the back scattering system for RFID.Already, RFID systems have been employed extensively as means ofwireless communication usable only in strictly localized applications.

The RFID system is a system which is made up of a tag and a reader andwhich causes the reader to read information from inside the tag innoncontact fashion. The RFID tag is a device that contains uniqueidentification information. Upon receipt of a radio wave at aparticularly frequency, the tag generates a radio wave at a modulationfrequency corresponding to the identification information held inside.The reader identifies the frequency thus generated by the RFID tag. Thetag and reader/writer communicate with each other using a method such aselectromagnetic coupling, electromagnetic induction, or radio frequencycommunication. This invention pertains to the radio frequencycommunication method that utilizes microwaves illustratively on a 2.4GHz band.

FIG. 1 is a schematic view showing a hardware structure of a wirelesscommunication apparatus 300 embodying the invention. This wirelesscommunication apparatus 300 may be a digital camera, a camera-equippedcellular phone, or like equipment that transmits picture data whileoperating primarily on batteries, not shown.

As a digital camera, the wireless communication apparatus 300 isconstituted illustratively by a camera unit 302, a signal processingunit 303, a memory card interface unit 304, an operation/display unit305, and a USB interface unit 306.

The signal processing unit 303 converts picture data coming from thecamera unit 302 into JPEG (Joint Photographic Experts Group) or someother suitable format. The picture data thus converted is placed into anexternal memory card 307 for storage through the memory card interface304.

The operation/display unit 305 provides picture displays and allowsnecessary settings to be made. The USB (universal serial bus) interfaceunit 306 is used to transfer picture data from the camera to a PCthrough a USB interface.

As its wireless transmission module 308, the wireless communicationapparatus 300 of this embodiment uses a radio frequency type RFID tag.

The wireless transmission module 308 is made up of an antenna 309, radiofrequency switches 310 and 311, a band-pass filter 312, and an ASKdetection unit 313. This embodiment utilizes the 2.4 GHz band for itsradio frequency.

In data transmissions including picture transfers, the radio frequencyswitch 311 is turned off along with the ASK detection unit 313 fortransition into an open state in response to control signals from thesignal processing unit 303. The wireless transmission module 308receives picture data retrieved from the memory card 307 by the signalprocessing unit 303. Upon receipt of the retrieved picture data, thewireless transmission module 308 turns on or off the other radiofrequency switch 310 connected to the antenna 309 in keeping with a bitimage of the received data. For example, if the data is “1,” the radiofrequency switch 310 is turned on; if the data is “0,” the switch 310 isturned off.

When the radio frequency switch 310 is on, the antenna 309 isshort-circuited to ground to let a radio wave coming from a transferdestination (discussed later) be absorbed thereby, as illustrated. Whenthe radio frequency switch 310 is off, the antenna 309 is left open sothat the radio wave coming from the transfer destination is reflected.The operation of turning on and off the radio frequency switch 310generates reflected waves with their phases 180 degrees apart inresponse to the incoming radio wave. That means the transfer destinationcan read a transmitted data signal such as picture data by detectingreflected phases of the incoming radio wave.

More specifically, with the back scattering system in effect, picturedata is transmitted as reflected waves obtained by subjecting to PSK(phase shift keying) modulation the incoming radio wave generatedthrough fluctuations in antenna load impedance as a result of turning onand off a radio frequency switch arrangement. The reflected wave signalfrom the wireless transmission module 308 is equivalent to aPSK-modulated wave.

The radio frequency switch 310 is generally composed of a GaAs IC thatconsumes scores of 10 μW or less of power. The communication methodabove thus provides wireless picture transmission at very low levels ofpower dissipation.

At the time of data reception, the radio frequency switch 311 is turnedon along with the ASK detection unit 313 by control signals coming fromthe signal processing unit 303.

The band-pass filter 312 and ASK detection unit 313 are used to receivean ASK-modulated transmission acknowledge signal from the transferdestination. These two blocks are not needed if the transmission takesplace on a one-way basis, i.e., without expecting acknowledgement. Ifacknowledgement is required, the control processes involved are carriedout by the signal processing unit 303.

The band-pass filter 312 is used to let the incoming radio wave pass onthe 2.4 GHz frequency band while attenuating signal components on anyother frequency band. In acknowledging the transmission, the ASKdetection unit 313 consumes 30 mW or less of power.

As a result, the average power dissipation during transmission of datasuch as pictures by the wireless communication apparatus of FIG. 1amounts to 10 mW or less for the two-way communication setup involvingacknowledgement and scores of 10 μW for the one-way data transmissionwithout the need for acknowledgement. These levels of power dissipationare dramatically lower than those consumed on average by ordinarywireless LAN systems.

This invention also pertains to a wireless communication apparatus fortransmitting data at a low level of power dissipation under the backscattering system utilizing reflection of incoming radio waves. Theinvention may be practiced otherwise by use of QPSK (quadrature phaseshift keying) for the modulation of reflected waves by the wirelesstransmission module 308. The PSK method is replaced by the QPSK methodfor the purpose of boosting the speed of data transmission. Whereas PSKmodulation requires assigning “0” and “1” to two phases 180 degreesapart, QPSK modulation involves assigning (0,0), (0, 1), (1, 0) and(1, 1) to phases 0, π/2, π and 3π/2 respectively for data transmission,the phases being π/2 apart from one another. The latter modulationmethod thus increases the bit rate appreciably. Generally, 2^(n) phasePSK modulation entails assigning data to 2^(n) phases that are π/2^(n−1)apart from one another. That means, in simplified terms, the bit rate ismade higher the greater the value of n.

FIG. 2 is a schematic view indicating a typical structure of thewireless communication apparatus. The wireless transmission module 308includes an antenna 309, a radio frequency switch 311, a band-passfilter 312, and an ASK detection unit 313 all functioning in the samemanner as their counterparts in the apparatus of FIG. 1. The wirelesstransmission module 308 also includes phase shifters 320, 321, and 322connected in series to the antenna 309, as well as radio frequencyswitches 323, 324, 325 and 326 and a data decoder 327.

As described above, the back scattering system brings about datatransmission by alternating absorption and reflection of incoming radiowaves through on/off changeovers of radio frequency switches. Becausethe radio frequency switches 323, 324 and 325 can only be switched atlimited speeds, it is necessary to forward information in a plurality ofbits at each changeover for high-speed data transmission.

The phase shifters 320, 321 and 322 may each be formed by a linearrangement such as a strip line providing a λ (wavelength)/8 shift onthe 2.4 GHz frequency band, or by an active phase shifter capable ofvarying its phase under voltage control. The phase shifters 320, 321 and322 each generate a phase difference of 45 degrees for one-way wavepassage and a phase difference of 90 degrees for two-way wave passage.Because the phase shifters 320, 321 and 322 are connected in series tothe antenna 309, turning on and off the radio frequency switches 323,324, 325 and 326 in different combinations provides different signalchannels over which reflected waves of the incoming radio wavereciprocate. This arrangement gives four phase differences to thereflected waves.

For example, if the radio frequency switch 323 alone is turned on, theincoming radio wave is reflected at point “a” in FIG. 2. If the radiofrequency switch 324 alone is turned on, the incoming radio wave isreflected at point “b” but the phase of the incoming wave is shifted by90 degrees relative to that of the reflected wave at point “a” becauseof wave passage through the phase shifter 320. If the radio frequencyswitch 325 alone is turned on, the incoming radio wave is reflected atpoint “c” but the phase of the incoming wave is shifted by 180 degreesrelative to that of the reflected wave at point “a” because of wavepassage through the phase shifters 320 and 321. If the radio frequencyswitch 326 alone is turned on, the incoming radio wave is reflected atpoint “d” but the phase of the incoming wave is shifted by 270 degreesrelative to that of the reflected wave at point “a” because of wavepassage through the phase shifters 320, 321 and 322. That is, turning onany one of the radio frequency switches 323, 324, 325 and 326alternatively can generate reflected waves with their four phases 90degrees apart from one another.

For data transmissions such as picture transfers, the radio frequencyswitch 311 is turned off along with the ASK detection unit 313 fortransition into an open state under control of the signal processingunit 303. The wireless transmission module 308 performs QPSK modulationby dividing data into increments of two bits, each increment beingassigned a phase corresponding to the varying two-bit 0/1 combination.

More specifically, upon receipt of picture data read from the memorycard 307 by the signal processing unit 303, the wireless transmissionmodule 308 forwards bit images of the retrieved data to the data decoder327. The data decoder 327 divides the received data into increments oftwo bits so as to turn on the radio frequency switch 323 alone if thedata image is “00,” to turn on the radio frequency switch 324 alone ifthe data image is “01,” to turn on the radio frequency switch 325 if thedata image is “11,” and to turn on the radio frequency switch 326 aloneif the data image is “10.”

When the data is “00,” the radio frequency switch 323 alone is turnedon. This causes the incoming radio wave to be reflected at point “a.”

When the data is “01,” the radio frequency switch 324 alone is turnedon. This causes the incoming radio wave to be reflected at point “b.”Because of its passage through the phase shifter 320, the reflected wavehas its phase shifted by 90 degrees relative to that of the reflectedwave at point “a.”

When the data is “11,” the radio frequency switch 325 alone is turnedon. This causes the incoming radio wave to be reflected at point “c.”Because of its passage through the phase shifters 320 and 321, thereflected wave has its phase shifted by 180 degrees relative to that ofthe reflected phase at point “a.”

When the data is “10,” the radio frequency switch 326 alone is turnedon. This causes the incoming radio wave to be reflected at point “d.”Because of its passage through the phase shifters 320, 321 and 322, theincoming radio wave has its phase shifted by 270 degrees relative tothat of the reflected wave at point “a.”

In this manner, it is possible to generate QPSK-modulated reflectedwaves having four different phases 90 degree apart from one another inkeeping with the varying two-bit value of data.

It is also possible for the wireless transmission module 308 of FIG. 2to carry out PSK modulation. In this case, the radio frequency switches324 and 326 are left uncontrolled. When the data is “0,” the radiofrequency switch 323 is turned on; when the data is “1,” the radiofrequency switch 325 is turned on so as to shift the phase of thereflected wave by 180 degrees relative to the phase in effect when thedata is “0.” That is, the same circuit can handle two modulationmethods, QPSK and PSK. The two methods can be alternated dynamicallyduring communication.

It will be appreciated that in addition to data communicationapplications, the inventive method of FIG. 2 for creating multiphasemodulated waves is also effective for general RFID applications where nopower supply is furnished.

Upon receipt of an incoming radio wave, the radio frequency switch 311is turned on along with the ASK detection unit 313 under control of thesignal processing unit 303. Furthermore, the radio frequency switches323, 324 and 326 are turned off while the radio frequency switch 325alone is turned on. With these settings in effect, the incoming, signalfrom the antenna 308 is input to the ASK detection unit 313 via theband-pass filter 312 with a minimum of losses.

The band-pass filter 312 and ASK detection unit 313 are used to receivean ASK-modulated transmission acknowledge signal from the transferdestination. These two blocks are not necessary if the transmissiontakes place on a one-way basis with no need for acknowledgement. Ifacknowledgement is required, the control processes involved are carriedout by the signal processing unit 303.

In another variation of the wireless communication apparatus of FIG. 2under the back scattering system adopting QPSK modulation, seven λ/16phase shifters and eight radio frequency switches may be connected inthe same manner as in the preceding example. This setup provides aneight-phase PSK modulation arrangement whereby eight reflected waveswith their phases 45 degrees apart from one another are assigned toeight data bit patterns ranging from “000” to “111.”

FIG. 3 is a schematic view depicting a typical structure of a wirelesscommunication apparatus operating under a back scattering systemadopting eight-phase PSK modulation. The apparatus of FIG. 3 includes awireless transmission module 508 made up of an antenna 509, a radiofrequency switch 511, a band-pass filter 512, and an ASK detection unit512 all functioning in the same manner as their counterparts in theapparatus of FIG. 1. The wireless communication apparatus of FIG. 3 alsoincludes seven phase shifters 521, 522, 523, . . . , 527 connected inseries to the antenna 509; radio frequency switches 531, 532, 533, . . ., 538; and a data decoder 540.

As described above, the back scattering system implements datatransmission by alternating absorption and reflection of incoming radiowaves through on/off changeovers of radio frequency switches. Becausethe radio frequency switches 531, 532, 533, etc., can only be switchedat limited speeds, it is necessary to forward information in a pluralityof bits at each changeover for high-speed data transmission.

The phase shifters 521, 522, 523, . . . , 527 may each be formed by aline arrangement such as a strip line providing a λ/16 shift on the 2.4GHz frequency band, or by an active phase shifter capable of varying itsphase under voltage control. The phase shifters 521, 522, 523, . . . ,527 each generate a phase difference of 27.5 degrees for one-way wavepassage and a phase difference of 45 degrees for two-way wave passage.Thus turning on and off the radio frequency switches 531, 532, 533, . .. , 538 in different combinations provides different signal channelsover which reflected waves of the incoming radio wave reciprocate. Thisarrangement gives eight phase differences to the reflected waves.

For example, if the radio frequency switch 531 alone is turned on, theincoming radio wave is reflected at point “a” in FIG. 3. If the radiofrequency switch 532 alone is turned on, the incoming radio wave isreflected at point “b” but the phase of the incoming wave is shifted by45 degrees relative to that of the reflected wave at point “a” becauseof wave passage through the phase shifter 521. If the radio frequencyswitch 533 alone is turned on, the incoming radio wave is reflected atpoint “c” but the phase of the incoming wave is shifted by 90 degreesrelative to that of the reflected wave at point “a” because of wavepassage through the phase shifters 521 and 522. Likewise, if the radiofrequency switch 538 alone is turned on, the incoming radio wave isreflected at point “h” but the phase of the incoming wave is shifted by315 degrees relative to that of the reflected wave at point “a” becauseof wave passage through all seven phase shifters 521 through 527. Thatis, turning on any one of the radio frequency switches 531, 532, 533, .. . , 538 alternatively can generate reflected waves with their eightphases 45 degrees apart from one another.

For data transmissions such as picture transfers, the radio frequencyswitch 511 is turned off along with the ASK detection unit 513 fortransition into an open state under control of the signal processingunit 503. The wireless transmission module 508 performs eight-phase PSKmodulation by dividing data into increments of three bits, eachincrement being assigned a phase corresponding to the varying three-bit0/1 combination.

More specifically, upon receipt of picture data read from the memorycard 307 by the signal processing unit 503, the wireless transmissionmodule 508 forwards bit images of the retrieved data to the data decoder540. The data decoder 540 divides the received data into increments ofthree bits so as to turn on the radio frequency switch 521, alone if thedata image is “000,” to turn on the radio frequency switch 522 alone ifthe data image is “001,” to turn on the radio frequency switch 523 ifthe data image is “011,” and so on.

When the data is “000,” the radio frequency switch 531 alone is turnedon. This causes the incoming radio wave to be reflected at point “a.”When the data is “001,” the radio frequency switch 532 alone is turnedon. This causes the incoming radio wave to be reflected at point “b.”Because of its passage through the phase shifter 521, the reflected wavehas its phase shifted by 45 degrees relative to that of the reflectedwave at point “a” where the data is “000.”

When the data is “011,” the radio frequency switch 533 alone is turnedon. This causes the incoming radio wave to be reflected at point “c.”Because of its passage through the phase shifters 521 and 522, thereflected wave has its phase shifted by 90 degrees relative to that ofthe reflected phase at point “a” where the data is “000.”

When the data is “010,” the radio frequency switch 534 alone is turnedon. This causes the incoming radio wave to be reflected at point “d.”Because of its passage through the phase shifters 521, 522 and 523, theincoming radio wave has its phase shifted by 135 degrees relative tothat of the reflected wave at point “a” where the data is “000.” Theswitching operation entailing radio wave reflection proceeds in likemanner.

As described, it is possible to generate eight-phase PSK-modulatedreflected waves having eight different phases 45 degree apart from oneanother in keeping with the varying three-bit value of data.

It is also possible for the wireless transmission module 508 of FIG. 3to carry out PSK modulation. In this case, all radio frequency switchesexcept for the switches 531 and 534 are left uncontrolled. When the datais “0,” the radio frequency switch 531 is turned on; when the data is“1,” the radio frequency switch 534 is turned on so as to shift thephase of the reflected wave by 180 degrees relative to the phase ineffect when the data is “0.” That is, the same circuit can handle twomodulation methods, eight-phase QPSK and PSK. The two methods can bealternated dynamically during communication.

It will be appreciated that in addition to data communicationapplications, the inventive method of FIG. 3 for creating multiphasemodulated waves is also effective for general RFID applications where nopower supply is furnished.

Upon receipt of an incoming radio wave, the radio frequency switch 511is turned on along with the ASK detection unit 513 under control of thesignal processing unit 503. Furthermore, only one of the radio frequencyswitches 531 through 538 is turned on and the other switches are leftoff. With these settings in effect, the incoming signal from the antenna508 is input to the ASK detection unit 513 via the radio frequencyswitch 511 and band-pass filter 512 with a minimum of losses.

The band-pass filter 512 and ASK detection unit 513 are used to receivean ASK-modulated transmission acknowledge signal from the transferdestination. These two blocks are not necessary if the transmissiontakes place on a one-way basis with no need for acknowledgement. Ifacknowledgement is required, the control processes involved are carriedout by the signal processing unit 503.

FIG. 4 is a schematic view indicating another structure of the wirelesscommunication apparatus operating under the back scattering systemadopting QPSK modulation. Whereas the apparatus of FIG. 2 has itsreflection points formed by grounding, the apparatus of FIG. 4 arefurnished, by contrast, with reflection points formed by an opentermination each.

The wireless communication apparatus 308 in FIG. 4 is made up of anantenna 309; radio frequency switches 330, 332 and 334; phase shifters331, 333 and 335 connected in series; and a data decoder 336. Forpurpose of simplification and illustration, the radio frequency switch311, band-pass filter 312, and ASK detection unit 313 constituting thereception block in FIG. 2 are omitted from FIG. 4.

The phase shifters 331, 333 and 335 may each be formed by a linearrangement such as a strip line providing a λ/8 shift on the 2.4 GHzfrequency band, or by an active phase shifter capable of varying itsphase under voltage control. The phase shifters each generate a phasedifference of 45 degrees for one-way wave passage and a phase differenceof 90 degrees for two-way wave passage. Thus turning on and off theradio frequency switches 330, 332 and 334 in different combinationsprovides different signal channels over which reflected waves of theincoming radio wave reciprocate. This arrangement gives four phasedifferences to the reflected waves.

For example, if the radio frequency switch 330 is turned off, theincoming radio wave is reflected at point “a” in FIG. 4. If the radiofrequency switch 330 is turned on and the radio frequency switch 332 isturned off, the incoming radio wave is reflected at point “b” but thephase of the incoming wave is shifted by 90 degrees relative to that ofthe reflected wave at point “a” because of wave passage through thephase shifter 331. If the radio frequency switches 330 and 332 areturned on and the radio frequency switch 334 is turned off, the incomingradio wave is reflected at point “c” but the phase of the incoming waveis shifted by 180 degrees relative to that of the reflected wave atpoint “a” because of wave passage through the phase shifters 331 and333. If the radio frequency switches 330, 332 and 334 are all turned on,the incoming radio wave is reflected at point “d” but the phase of theincoming wave is shifted by 270 degrees relative to that of thereflected wave at point “a” because of wave passage through the phaseshifters 331, 333 and 335. That is, turning on and off the radiofrequency switches 330, 332 and 334 in different combinations cangenerate reflected waves with their four phases 90 degrees apart fromone another.

In executing picture transfers, the wireless transmission module 308performs QPSK modulation by dividing data into increments of two bits,each increment being assigned a phase corresponding to the varyingtwo-bit 0/1 combination.

More specifically, upon receipt of picture data read from the memorycard 307 by the signal processing unit 303, the wireless transmissionmodule 308 forwards bit images of the retrieved data to the data decoder336. The data decoder 336 divides the received data into increments oftwo bits so as to turn on the radio frequency switch 330 if the dataimage is “00,” to turn on the radio frequency switch 330 and turn offthe radio frequency switch 332 if the data image is “01,” to turn on theradio frequency switches 330 and 332 and turn off the radio frequencyswitch 334 if the data image is “11,” and to turn on all radio frequencyswitches 330, 332 and 334 when the data image is “10.”

When the data is “00,” the radio frequency switch 330 is turned off.This causes the incoming radio wave to be reflected at point “a.”

When the data is “01,” the radio frequency switch 330 is turned on andthe radio frequency switch 332 is turned off. This causes the incomingradio wave to be reflected at point “b.” Because of its passage throughthe phase shifter 331, the reflected wave has its phase shifted by 90degrees relative to that of the reflected wave at point “a” where thedata is “00.”

When the data is “11,” the radio frequency switches 330 and 332 areturned on and the radio frequency switch 334 is turned off. This causesthe incoming radio wave to be reflected at point “c.” Because of itspassage through the phase shifters 331 and 333, the reflected wave hasits phase shifted by 180 degrees relative to that of the reflected phaseat point “a” where the data is “00.”

When the data is “10,” all radio frequency switches 330, 332 and 334 areturned on. This causes the incoming radio wave to be reflected at point“d.” Because of its passage through the phase shifters 331, 333 and 335,the incoming radio wave has its phase shifted by 270 degrees relative tothat of the reflected wave at point “a” where the data is “00.”

As described, it is possible to generate QPSK-modulated reflected waveshaving four different phases 90 degree apart from one another in keepingwith the varying two-bit value of data.

FIG. 5 is a schematic view presenting a hardware structure of a wirelesscommunication apparatus for receiving data from the wirelesscommunication apparatus of FIG. 2 or FIG. 4. The apparatus of FIG. 5represents a picture reproducer such as a PC, a TV set, or a printerthat displays or outputs received picture data.

The apparatus of FIG. 5 is fed with picture data by use of reflectedwaves. This requires a wireless reception module 400 to transmit anunmodulated carrier for producing reflected waves. The wirelessreception module 400 is made up of an antenna 401 for the 2.4 GHzfrequency band, a circulator 402, a reception unit 403, a transmissionunit 406, a frequency synthesizer 409, a communication control unit 410,and a host interface unit 411. The reception unit 403 includes anorthogonal detection unit 404 and an AGC (auto gain control) amplifier405. The transmission unit 406 includes a mixer 408 and a poweramplifier 407. The host interface unit 411 is connected to a host device412 such as a CP to which received picture data is transferred throughthe interface.

The wireless reception module 400 transmits the unmodulated carrier whenthe communication control unit 410 applies a predetermined DC voltage tothe mixer 408. The frequency of the unmodulated carrier to betransmitted is determined by the frequency of the frequency synthesizerunder control of the communication control unit 410. The apparatus ofFIG. 5 utilizes the 2.4 GHz frequency band. The unmodulated carrieroutput by the mixer 408 is, amplified by the power amplifier 407 up to apredetermined level. The amplified carrier is emitted from the antenna401 via the circulator 402.

The reflected wave coming from a picture transmission apparatus 300 hasthe same frequency as that which is transmitted by the aforementionedwireless reception module 400. The reflected wave is received by theantenna 401 and input to the reception unit 403 via the circulator 402.Because the orthogonal detection unit 404 is fed with a local frequencythat is the same as the transmission frequency, a PSK- or QPSK-modulatedwave derived from the modulation process by the picture transmissionapparatus 300 appears at the output of the orthogonal detection unit404. Because the incoming signal has a phase that differs from that ofthe local signal, the orthogonal detection unit 404 outputs itsmodulated signals as an I-axis signal and a Q-axis signal in keepingwith the phase difference between the incoming and the local signals.

The AGC amplifier 405 controls its input I-axis and Q-axis signalsoptimally in gain before sending the gain-controlled signals to thecommunication control unit 410. Given the I-axis and Q-axis signals, thecommunication control unit 410 performs PSK or QPSK demodulation wherebythe carrier and clock signal are reproduced. The correctly reproduceddata is transferred to the host device 412 via the host interface unit411.

If the data transmission from the picture transmission device 300 needsto be acknowledged, the communication control unit 410 transfers to themixer 408 either ACK (acknowledgement) digital data if the receivedpacket data is correct or NACK (negative acknowledgement) digital dataif the received packet data is not correct. The transferred ACK or NACKdigital data is subjected to ASK modulation. Whether or not the receiveddata is correct is determined by verifying CRC (cyclic redundancy check)code attached to the picture data packets received.

FIG. 6 shows a typical control sequence in effect when the wirelesscommunication apparatus 300 of FIG. 2 or FIG. 4 acting as a picturetransmission device communicates data wirelessly with the wirelesscommunication apparatus 400 of FIG. 5 working as a picture displaydevice. The setup of FIG. 6 assumes that each transmission from oneapparatus is acknowledged by the other apparatus. The control sequenceis described below.

(Step 1)

In the picture transmission device, data transmission mode isestablished illustratively by the user.

(Step 2)

Likewise in the picture display device, data reception wait mode isestablished illustratively by the user.

(Step 3)

The picture display device as the destination for picture transferstransmits an unmodulated carrier by which the picture transmissiondevice produces reflected waves.

(Step 4)

The picture transmission device having received the unmodulated carriermakes a data transmission request using reflected waves.

(Step 5)

The picture display device having received the data transmission requestreturns permission to send through ASK modulation.

(Step 6)

The picture display device transmits the unmodulated carrier forreflected wave formation.

(Step 7)

On receiving the unmodulated carrier, the picture transmission devicetransmits packetized data using reflected waves. In this step, thepicture transmission device performs QPSK modulation by dividing datainto increments of two bits, each increment being assigned a phasecorresponding to the varying two-bit 0/1 combination (as discussedabove).

(Step 8)

The picture display device subjects the received packetized data to QPSKdemodulation thereby restoring the initial data. If the received data isfound correct, the picture display device returns an ACK(acknowledgement) signal through ASK modulation; if the received data isnot found correct, the picture display device returns a NACK (negativeacknowledgement) signal. Whether or not the data is correct isdetermined by verifying CRC (cyclic redundancy check) code attached tothe data packets received.

When transmitting the ACK or NACK signal, the picture display device mayinclude in the same signal a command addressed to the picturetransmission device. Illustratively, the picture display device may senda slide show request command to the picture transmission device.

In the manner described above, the picture display device can controlthe picture transmission device from a remote location. If the picturedisplay device is a TV set that can be, operated by an infrared rayremote controller, it is possible to send a command from the remotecontroller to the picture display device which in turn forwards thecommand to the picture transmission device. That is, the picturetransmission device can be controlled indirectly by use of the infraredray remote controller.

Steps 6 through 8 are then repeated until all data has been transmitted.

In the control sequence described above, communications are conducted ona two-way basis so that the picture data is acknowledged when normallytransmitted. Alternatively, communications may be performed on a one-waybasis in the case of streaming data transfers from a video camera orlike sources. Adopting the one-way transmission setup eliminates theneed for the picture display device to return ASK-modulatedacknowledgement signals. It is also unnecessary for the picturetransmission device to receive the acknowledgement signals, whichtranslates into further savings in power dissipation.

It will be appreciated that in executing the control sequence of FIG. 6,the picture transmission device has no need for an oscillator.

In the setup of FIG. 1, the picture transmission device such as adigital camera incorporates the wireless transmission module 308.However, this is not limitative of the invention. Alternatively, thewireless transmission module may be furnished as a detachable adapterconnected externally to the inventive apparatus through USB (universalserial bus) or other suitable interfaces.

FIG. 7 schematically shows a typical structure of a wirelesstransmission module furnished as an adapter type module.

As illustrated, the picture transmission device in FIG. 7 includes acamera unit 602, a signal processing unit 603, a memory card interfaceunit 604, an operation/display unit 605, a USB interface unit 606, and amemory card 607. These components are substantially the same as theircounterparts 202 through 207 of the conventional wireless LAN-capabledigital camera shown in FIG. 6.

Generally, the USB interface unit 606 works as a slave. After readingpicture data of interest from the memory card 607 through the memorycard interface unit 604, the signal processing unit 603 transfers theretrieved data through the USB interface unit 606 to a PC (USB host)over a USB cable. In the setup of FIG. 4, the USB interface unit isswitched to the host side when connected to a wireless transmissionmodule 601 in a slave device that is attached externally through the USBinterface. This setup is equivalent to the apparatus shown in FIG. 1.

The wireless transmission module 601 may be an adapter equipped with aUSB connector and an antenna 609, illustratively taking the shape of adevice indicated by reference numeral 620.

The wireless transmission module 601 shown in FIG. 4 is substantiallythe same as the wireless transmission module 308 depicted in FIG. 2 orFIG. 4, except that it is additionally provided with a USB interfaceunit 614.

Upon transmission of picture data, the radio frequency switch 311 isturned off along with the ASK detection unit 313 for transition into anopen state under control of the signal processing unit 303. The wirelesstransmission module 308 receives the picture data retrieved from thememory card 607, by way of the host side USB interface unit 606 andslave-side USB interface unit 614. In this manner, it is possible togenerate four reflected waves with four different phases 90 degreesapart from one another in accordance with the varying value of two-bitdata. This system provides reflected waves through QPSK modulation, asdiscussed earlier. Illustratively, when the data is “01,” the reflectedwave has its phase shifted by 90 degrees; when the data is “11,” thereflected wave has its phase shifted by 180 degrees; when the data is“10,” the reflected wave has its phase shifted by 270 degrees.

Upon data reception, the band-pass filter and ASK detection unit areused to receive the ASK-modulated acknowledgement signal from thetransfer destination (as discussed above). These two blocks are notnecessary if the transmission takes place on a one-way basis with noneed for acknowledgement. If acknowledgement is required, the controlprocesses involved are executed by a communication control unit 608. Aband-pass filter 612 is used to let the incoming radio wave pass on the2.4 GHz frequency band while attenuating signal components on any otherfrequency band.

The setup of FIG. 7, as with the apparatus shown in FIG. 1, permitspicture data transmission at very low levels of power dissipation. Asthe mobile device is getting progressively smaller to meet today'sneeds, the adapter type wireless transmission module like theabove-described embodiment of the invention is considered particularlyeffective. Although this embodiment utilizes the USB interface forconnection with the wireless communication apparatus such as a digitalcamera, this is not limitative of the invention. Any other suitableinterface may be adopted instead.

FIG. 8 schematically depicts another typical structure of the wirelesstransmission module 308 for use with the wireless communicationapparatus adopting QPSK modulation.

The wireless communication module 308 in FIG. 8 includes an antenna 901,synthesizing/distributing unit 902, radio frequency switches 903 and905, a λ/8 phase shifter 904 connected serially to the radio frequencyswitch 905, and a serial/parallel converter 906. For purpose ofsimplification and illustration, the radio frequency switch 311,band-pass filter 312, and ASK detection unit 313 constituting thereception block in FIG. 2 are omitted from FIG. 8.

A signal channel branched by the synthesizing/distributing unit 902 andgrounded via the radio frequency switch 903, and a signal channelgrounded via the phase shifter 904 and radio frequency switch 905 eachconstitute a reflected signal channel for back scattering typecommunication. That is, the radio frequency switch 903 acts as a BPSKmodulator; likewise the phase shifter 904 and radio frequency switch 905operate as another BPSK modulator.

The latter BPSK modulator, having a λ/8 phase delay produced by thephase shifter 904, provides a phase difference of λ/4 for two-way wavepassage. That means BPSK modulation is carried out on an axis 90 degreesapart from the axis of the former BPSK modulator. This arrangement isequivalent to implementing QPSK modulation, because the radio frequencyswitch 903 performs BPSK modulation on the I axis while the phaseshifter 904 and radio frequency switch 905 carry out BPSK modulation onthe Q axis. The synthesizing/distributing unit 902 is used here forsignal bifurcation and synthesis.

In the embodiment described above, one of the two radio frequencyswitches 903 and 905 is short-circuited to ground in the actualcircuitry. Alternatively, a short-circuit may be formed by use of a λ/4open stub arrangement.

The two carriers formed by the synthesizing/distributing unit 902bifurcating what has been received from the antenna 901 are subjected toQPSK modulation, one carrier being modulated by the radio frequencyswitch 903, the other carrier by the phase shifter 904 and radiofrequency switch 905. The reflected signals thus modulated are againemitted from the antenna 901 via the synthesizing/distributing unit 902.

The serial/parallel converter 906 converts serially transmitted datainto I and Q parallel signals.

More specifically, when the two bits of data following theserial/parallel conversion are “00,” the radio frequency switches 903and 905 are both turned off; when the two data bits are “01,” the radiofrequency switch 903 alone is turned on; when the data bits are “11,”the radio frequency switch 905 alone is turned on; when the data bitsare “10,” the radio frequency switches 903 and 905 are both turned on.

Japanese Paten Laid-open No. Hei 10-209914 proposes a duplex wirelesscommunication system including an interrogator and a plurality of tagspositioned spatially apart from the interrogator. The interrogator ofthe proposed system transmits a carrier wave (CW) radio signal to atleast one of the tags within the system whereby a subcarrier signal isQPSK-modulated in keeping with information signals. It should be notedthat the proposed system performs ASK modulation in a secondarymodulation stage (e.g., see FIG. 3 of the Application) using asubcarrier signal having undergone QPSK modulation in the primarymodulation stage. In this case, the actual transmission rate is limitedby the performance of the ASK modulation method in use. In other words,the QPSK modulation setup adopted by the proposed system does notcontribute to any improvement in the transmission rate. The proposedsystem further entails problems associated with DC offset and mixernoises. According to the present invention, by contrast, the maincarrier is QPSK-modulated on the principle that reflected signalchannels provide phase differences by allowing the incoming radio waveto reciprocate thereon. Thus there exists a clear difference instructure between the proposed system of the above-cited Application andthis invention.

INDUSTRIAL APPLICABILITY

It is to be understood that while the invention has been described inconjunction with specific embodiments with reference to the accompanyingdrawings, it is evident that many alternatives, modifications andvariations will become apparent to those skilled in the art in light ofthe foregoing description without departing from the spirit or scope ofthe invention.

This invention pertains to a multiphase modulation method utilizingphase differences that occur between a plurality of reflected signalchannels furnished in a manner constituting a back scattering typecommunication setup. The description above has primarily dealt with anRFID system having a reader reads information from inside tags innoncontact fashion. However, that embodiment is not limitative of theinvention. In addition to data transmission applications, the inventivesystem is obviously effective when used in general RFID applications inwhich no power source is provided.

Thus the specificities contained in this description should not beconstrued as limiting the scope of the invention but as merely providingillustrations of some of the presently preferred embodiments of thisinvention. Accordingly, the scope of the invention should be determinedby the appended claims and their legal equivalents, rather than by theexamples given.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1]

FIG. 1 is a schematic view showing a hardware structure of a wirelesscommunication apparatus 300 embodying the invention;

[FIG. 2]

FIG. 2 is a schematic view indicating a typical structure of a wirelesscommunication apparatus operating under a back scattering systemadopting QPSK modulation;

[FIG. 3]

FIG. 3 is a schematic view depicting a typical structure of a wirelesscommunication apparatus operating under a back scattering systemadopting eight-phase PSK modulation;

[FIG. 4]

FIG. 4 is a schematic view indicating another structure of the wirelesscommunication apparatus adopting QPSK modulation;

[FIG. 5]

FIG. 5 is a schematic view presenting a hardware structure of a wirelesscommunication apparatus for receiving data from the wirelesscommunication apparatus of FIG. 2 or FIG. 4;

[FIG. 6]

FIG. 6 is a control sequence diagram outlining a typical controlsequence in effect when the wireless communication apparatus 300 of FIG.2 or FIG. 4 acting as a picture transmission device communicates datawirelessly with the wireless communication apparatus 400 of FIG. 5working as a picture display device;

[FIG. 7]

FIG. 7 is a schematic view showing a typical structure of a wirelesstransmission module furnished as an adapter type module;

[FIG. 8]

FIG. 8 is a schematic view depicting a typical structure of anotherwireless transmission module 308 for use with a wireless communicationapparatus adopting QPSK modulation; and

[FIG. 9]

FIG. 9 is a schematic view indicating a typical structure of aconventional RFID system.

DESCRIPTION OF REFERENCE CHARACTERS

-   300: wireless communication apparatus-   302, 602 . . . Camera unit-   303, 603 . . . Signal processing unit-   304, 604 . . . Memory card interface unit-   305 . . . Operation/display unit-   306, 606 . . . USB interface unit 307, 607 . . . Memory card-   308 . . . Wireless transmission module-   309, 609 . . . Antenna-   310, 311, 323, 324, 325 . . . Radio frequency switch-   312 . . . Band-pass filter-   313 . . . ASK detection unit-   320, 321, 322 . . . Phase shifters-   330, 332, 334 . . . Radio frequency switches-   331, 333, 335 . . . Phase shifters-   400 . . . Wireless reception module-   401 . . . Antenna-   402 . . . Circulator-   403 . . . Reception unit-   404 . . . Orthogonal detection unit-   405 . . . AGC amplifier-   406 . . . Transmission unit-   407 . . . Power amplifier-   408 . . . Mixer-   409 . . . Frequency synthesizer-   410 . . . Communication control unit-   411 . . . Host interface unit-   412 . . . Host device-   901 . . . Antenna-   902 . . . Synthesizing/distributing unit-   903 . . . Radio frequency switch-   904 . . . λ/8 phase shifter-   905 . . . Radio frequency switch-   906 . . . Serial/parallel converter

1. A wireless communication apparatus for performing data communicationunder a back scattering system using reflection of incoming radio waves,said wireless communication apparatus comprising a data transmissionunit comprising: an antenna for receiving an incoming radio wave from adata transfer destination; as many as n signal channels wherein a k-thsignal channel gives a phase difference of (k−1)λ/2^(n−1) for one-waywave passage therethrough, where 1≦k≦n; and reflected wave forming meansfor forming reflected waves with as many as n different phases, byselecting any one of said signal channels in keeping with outgoing data;wherein said data transmission unit forms said outgoing data using aphase difference pattern of said reflected waves with regard to saidincoming radio wave.
 2. A wireless communication apparatus according toclaim 1, further comprising a first through an (n−1)th phase shiftereach giving a phase difference of λ/2^(n+1) for one-way wave passagetherethrough, the phase shifters being connected in series to saidantenna; wherein said n signal channels comprise a first signal channelfor acquiring a first reflected wave by getting said incoming radio wavedirectly reflected without wave passage through any of said phaseshifters, and a k-th signal channel for acquiring a k-th reflected wavehaving a phase shifted by (k−1)π/2^(n−1) relative to the phase of saidfirst reflected wave through two-way wave passage between said firstphase shifter and a (k−1)th phase shifter, where 1≦k≦n; and wherein saidreflected wave forming means performs 2^(n) phase PSK modulation bydividing said outgoing data into increments of 2^(n−1) bits each and byassigning phases to the reflected waves through selection of a signalchannel in keeping with combinations of 0's and 1's in the 2^(n−1) bits.3. A wireless communication apparatus according to claim 2, furthercomprising a first through an n-th reflection point located between saidantenna and said first phase shifter, between said (k−t)th phase shifterand said k-th phase shifter where 2≦k≦n−1, and downstream of said(n−1)th phase shifter; wherein said reflected wave forming meansperforms 2n phase PSK modulation by dividing said outgoing data intoincrements of 2^(n−1) bits each and by assigning phases to the reflectedwaves through switching of said reflection points in keeping withcombinations of 0's and 1's in the 2^(n−1) bits.
 4. A wirelesscommunication apparatus according to claim 3, wherein each of saidreflection points is formed either by grounding or by use of an opentermination.
 5. A wireless communication apparatus according to claim 4,further comprising a data reception unit constituted by a filter forallowing said incoming radio wave received by said antenna to pass on apredetermined frequency band, and by a data reception unit comprising awave detection unit for forming a signal; wherein said data transmissionunit and said data reception unit are switched alternately depending onwhether or not said outgoing data is transmitted.
 6. A wirelesscommunication apparatus according to claim 3, further comprising a datareception unit constituted by a filter for allowing said incoming radiowave received by said antenna to pass on a predetermined frequency band,and by a data reception unit comprising a wave detection unit forforming a signal; wherein said data transmission unit and said datareception unit are switched alternately depending on whether or not saidoutgoing data is transmitted.
 7. A wireless communication apparatusaccording to claim 2, further comprising a data reception unitconstituted by a filter for allowing said incoming radio wave receivedby said antenna to pass on a predetermined frequency band, and by a datareception unit comprising a wave detection unit for forming a signal;wherein said data transmission unit and said data reception unit areswitched alternately depending on whether or not said outgoing data istransmitted.
 8. A wireless communication apparatus according to claim 1,further comprising a first through a third phase shifter each giving aphase difference of λ/8 for one-way wave passage therethrough, the phaseshifters being connected in series to said antenna; wherein said nsignal channels comprise: a first signal channel for acquiring a firstreflected wave by getting said incoming radio wave directly reflectedwithout wave passage through any of said phase shifters; a second signalchannel for acquiring a second reflected wave having a phase shifted byπ/2 relative to the phase of said first reflected wave through two-waywave passage through said first phase shifter alone; a third signalchannel for acquiring a third reflected wave having a phase shifted by πrelative to the phase of said first reflected wave through two-way wavepassage through said first and said second phase shifters; and a fourthsignal channel for acquiring a fourth reflected wave having a phaseshifted by 3π/2 relative to the phase of said first reflected wavethrough two-way wave passage through said first through said third phaseshifters; and wherein said reflected wave forming means performs QPSKmodulation by dividing said outgoing data into increments of 2 bits eachand by assigning phases to the reflected waves through selection of asignal channel in keeping with combinations of 0 and 1 in the 2 bits. 9.A wireless communication apparatus according to claim 8, wherein saidreflected wave forming means performs PSK modulation using solely saidfirst and said third signal channels.
 10. A wireless communicationapparatus according to claim 9, further comprising a data reception unitconstituted by a filter for allowing said incoming radio wave receivedby said antenna to pass on a predetermined frequency band, and by a datareception unit comprising a wave detection unit for forming a signal;wherein said data transmission unit and said data reception unit areswitched alternately depending on whether or not said outgoing data istransmitted.
 11. A wireless communication apparatus according to claim8, further comprising a data reception unit constituted by a filter forallowing said incoming radio wave received by said antenna to pass on apredetermined frequency band, and by a data reception unit comprising awave detection unit for forming a signal; wherein said data transmissionunit and said data reception unit are switched alternately depending onwhether or not said outgoing data is transmitted.
 12. A wirelesscommunication apparatus according to claim 1, further comprising a datareception unit constituted by a filter for allowing said incoming radiowave received by said antenna to pass on a predetermined frequency band,and by a data reception unit comprising a wave detection unit forforming a signal; wherein said data transmission unit and said datareception unit are switched alternately depending on whether or not saidoutgoing data is transmitted.
 13. A wireless communication apparatus forperforming data communication under a back scattering system usingreflection of incoming radio waves, said wireless communicationapparatus comprising a data transmission unit comprising: an antenna forreceiving an incoming radio wave from a data transfer destination; afirst reflected signal channel made of a first radio frequency switch; asecond reflected signal channel made of phase modulating means giving aphase difference of λ/8 and a second radio frequency switch;serial/parallel converting means for converting outgoing data fromserial form into a parallel signal; and synthesizing/distributing meansfor distributing said incoming radio wave coming from said antenna tothe reflected signal channels and for synthesizing outputs from saidreflected signal channels; wherein activation and deactivation of eachof said radio frequency switches are controlled using two data itemsconstituting the data having undergone the serial/parallel conversion,so that said data transmission unit forms said outgoing data using aphase difference pattern of the reflected waves with regard to saidincoming radio wave.
 14. A wireless communication apparatus according toclaim 13, further comprising a data reception unit constituted by afilter for allowing said incoming radio wave received by said antenna topass on a predetermined frequency band, and by a data reception unitcomprising a wave detection unit for forming a signal; wherein said datatransmission unit and said data reception unit are switched alternatelydepending on whether or not said outgoing data is transmitted.